366 MB. F. O. BOWEK ON APOSPOBY IN PEBNS. 



la the case of Polystichum angulare, var. pulcherrimum, there 

 is a more extensive excision from the cycle. Here not only is 

 the formation of the prothallus independent of the formation of 

 spores, but it even originates quite apart from the sporangium 

 and sorus by a purely vegetative outgrowth of the tips of the 

 pinnules ; this may he represented graphically thus : — 



Diag. 5. 



Frothallus 



¥em,?lant> 



Lastly, it remains to compare this new phenomenon of apo' 

 spory in the Terns with similar cases in other plants. In 1876 

 it was shown by Pringsheim*, and also by Staid f, that if the 

 stalk of the sporogonium of certain Mosses (Hypnum cupressi- 

 forme, Amblystegium serpens, Bryum ccespiticium, Ceratodon pur- 

 pureus) he cut into short pieces and cultivated on damp soil, 

 protonemal filaments spring from single cells, and ultimately 

 produce moss-plants of the normal type. There is thus artifi- 

 cially induced, by the prevention of the formation of spores, a 

 direct transition from the sporophore generation to the oophore 

 by a purely vegetative process. If we discount the artificial 

 character of this phenomenon, it may be closely compared with 

 the examples of apospory in Ferns, above described. 



A second example, but one which does not correspond exactly 

 with the above, is that vegetative budding described by Groebel + 

 as occurring in plants of Isoetes lacustris and I. echinospora. In 

 these species a bud frequently takes the place of the sporangium, 

 and is seated in the fovea at the base of the leaf. The bud 

 develops as a normal shoot of the sporophore generation. It may 

 be concluded that in this case there is an excision from the cycle 



* Monatsber. d. Akad. d. Wiss. in Berlin, 1870. 



t Eot. Zeit. 1870, p. 089. % Bot. Zeit. 1879, p. 1. 



